Copper oxide insulation layer for thermoelectric devices



June 8, 1965 5, L ETAL 3,188,24Q COPPER OXIDE INSULATION LAYER FORTHERMOELECTRIC D EVICES Original Filed Nov. 16, 1959 age Patented June8, I96

3,188,240 CGPPER QXIDE INSULATIGN LAYER FOR TEERMOELECTREC DEVICES H.Sam Lee, Gardenia, and Thomas E. Rodgers, Burbank, (lalifl, assignors toNorthrop Corporation, llllcverly Hills, Caliil, a corporation ofCalifornia ontinuation of application Ser. No. 853,343, Nov. 16, 1959.This application Sept. 11, 1961, Ser. No. 139,329 1 Claim. (Ci. 1364)This application is a continuation of our copending application, SerialNo. 853,343, filed November 16, 1959, for a Thermal-ConductingElectrically-Insulating Commounting favorable the semiconducting elementthereof have electrical conducting properties.

thermal and unfavorable been developed to date.

Accordingly it is an object of this invention to provide constructionand economical to fabricate.

Although the characteristic features of the respectively, In thisembodiment the major portion of components 1448 constitute pure copperplate members while the semiconductor components of ingots 19 and 21constitute N and ingots constructed of bismuth telluride. It should beunderstood that these materials are used for purposes of illustrationonly and other suitable materials which are well known to those skilledin the art may be substituted therefor.

efiicient in operation, rugged in- The above components are assembled ina convention manner substantially as shown in FIGURE 1. Constrution ofthe device 12 is completed by a heat sink an radiation means 22. Themeans 22 includes a bolt men er 23 the head of which is attached to thebase plat 16 by soldering, timing or the like while its shank cal ries aplurality of fin members 24. Electrical power 1' fed into the two stagesof the device 12 through the ele( trical connectors 2626 and 27-27. Forpurposes 0 illustration it may be assumed that current is caused tlenter the device through the right hand connectors 2t and 27 and to exitvia the left hand connectors 26 and 27 Thus the upper ends of the ingotsI9 and 21, that is fllt ends located adjacent the bridge members 17 and18 constitute cold ends. Accordingly the bridge member: 17 and 18constitute cold junctions and the lower end: of the ingots I9 and 21constitute hot ends.

A vacuum tube, transistor or the like (not shown) which is to be cooledis mounted in good thermal contact on the upper bridge member 17 whilethe means 22 is mounted in a tunnel or passageway 25 through whichcooling air or other fluid is caused to circulate. Accordingly aselectrical current is caused to flow through the device 12 heat isabsorbed from any component mounted on the element 1'7 and transferredto the aforementioned cooling air via the means 22.

The connector members 14 and 15, also the lower bridge member 18, areconstructed in accordance with procedures disclosed herein. Inasmuch asthe methods of construction of the above members are identical, only theconstruction of one of the connector members 14 Will be described indetail. The various steps employed in preparing a member 14 aredescribed in detail and are illustrated in FIGURES 2-5.

A plate of pure copper 14a (FIGURE 2), having the same dimensions as oneof the members 14 (FIGURES 1 and 5), is first thoroughly cleaned toinsure the removal of grease, oxides or other organic matter therefrom.This may be accomplished by known methods using alcohol or methyl ethylketone. The plate is then etched with a solution of nitric acid for five(5) or ten (10) minutes. Care should be taken not to injure the majorfaces of the plate 14a since it is important that these surfaces bemaintained perfectly smooth.

The plate Ma is now washed with distilled Water, dried and immediatelyplaced in an electric furnace which has been preheated for at least ten(10) minutes to a temperature of 650-980 C. After the plate 14a isexposed to the aforementioned temperature for ten (10) minutes a coatingof copper oxide 28, the thickness of which is approximately 20-25 mils,is formed on the plate 14a to provide a composite plate Mb substantiallyas shown in FIGURE 3. The coating of copper oxide is subsequentlyremoved by any suitable means from all but one of the major side facesof the plate 14b to provide a copper and copper oxide plate as shown inFIGURE 4.

The plate Me is now quenched in a reducing solution containing methylalcohol (CH OH) and sodium borate (NilzO'ZBzOa'lOHgO) at a temperatureof 5 to 15 C. The reducing solution is prepared by admixing twentypercent (20%) methyl alcohol in five percent (5%) sodium boratesolution. The reducing solution acts to change a portion of the copperoxide into pure copper to provide a coating 29 of substantially purecopper on the exposed surface of the copper oxide as shown in FIGURE 5.The reaction of the reducing solution is represented by the followingformula:

Thus it will be seen that a thin coating 2? of pure cop per is bonded bychemical action to the exposed surface f the copper oxide layer 28.Alternately a reducing solun consisting of ethyl alcohol (CH -CH andidium borate or other well known reducing agents may employed. Also thelayer 28 of copper oxide and coatg 29 of pure copper may be applied tothe plate 14a I other methods, such as electroplating or vacuum coatgoperations. However, it has been found that the love operations, that isutilizing oxidation and reducing aerations, provide chemical bonds whichare muc suarior in applications of the above character.

Either of the above reducing operations provides a in film or coating 29the thickness of which is approxiately 0.3 mil. The same procedures arefollowed in reparing the connector members 15 and the lower bridge ember18. The copper oxide layer 23 has an electrical :sistance of 9004400ohms per square inch at such time i current is flowing in one directionand 20004080 ohms :r square inch when the current is flowing in thereverse lrection. Although the layer of copper oxide 28 conitutes a goodelectrical insulator it does not block the ow of heat therethrough andin fact constitutes a good lermal conductor.

The components 15, and 18 are assembled in the evice 12 substantially asshown in FIGURE 1. Spefically the faces of the connector members 14 andlower ridge member 18, that is the surfaces on which the coatlgs 2'8 and29 are processed, are secured together in face face relation. Also themembers 15 are positioned n and secured to the upper surface of the baseplate 1'6 ith the coating 29 contacting the plate 16. The elecicalterminals 26 and 27 are directly attached to the Jmponents 15 and 14,respectively.

In assembling the device 12 the copper coatings 29 rovide eflicientmeans whereby the components 14 and 8 may be readily secured together asby soldering or nning, the copper coating provides the same advantage 1attaching the components 15 to the base plate 16. The upper oxide layers28, positioned between the compo cuts 14 and 18 and between 15 and 16,provide good lectrical insulation and at the same time insure goodlermal conductivity therebetween. Thus it will be aparent that aselectrical current enters the device 12 trough the right hand connectors26 and 27 it is caused follow a predetermined flow path through thedevice 2, because of the insulating qualities of the copper oxide tyers28, and exit through the left hand connectors 26 nd 27. Also the copperoxide layers 28 insure that heat,

s generated at the upper and lower bridge members 17 and 13, is quicklyand efficiently transmitted to the radiation means 22 where it isdissipated into the aforementioned air stream. In the event thethermoelectric device 12 is a heater instead of a cooler, it is obviousthat heat is transmitted equally well in the opposite direction, i.e.,from radiation means 22 to upper bridge member 17 for example.

Thus it will be seen that mounting means for semiconducting componentsadapted to fulfill the various objects of the invention is provided.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features,it is to he understood that the invention is not limited to the specificfeatures shown, out that the means and construction herein disclosedcomprise a preferred form of putting the invention into effect, and theinvention is therefore claimed in any of its forms or modificationswithin the legitimate and valid scope of the appended claim.

What is claimed is:

A thermoelectric device comprising two ingots of semiconducting materialforming portions of different stages thereof, two cop-per connectormembers, means respectively bonding each of said connector members toone surface of each of said ingots, a coating of copper oxide bonded onthe outer face of one of said connector mem bers, a coating of copperbonded on the outer face only of said oxide coating, and additionalbonding means including a soldered joint bonding said copper coating tothe other connector member, whereby a good thermal conductive and poorelectrical conductive attachment is provided between said ingots.

References Cited by the Examiner UNITED STATES PATENTS 1,844,925 2/32Kohler 20452 2,543,331 2/5li Ok-olicsanyi 136-4 2,844,638 7/58Lindenblad 136-42 2,966,033 12/60 Hughel 623 2,970,449 2/61 Eichhorn 623FOREIGN PATENTS 587,490 4/47 Great Britain. 824,347 1 1/59 GreatBritain.

WINSTON A. DOUGLAS, Primary Examiner. JOHN H. MACK, Examiner.

